Effects of three reducing agents on pasting properties of stored rice

The effects of three reducing agents (dithiothreitol, ascorbic acid, and tea polyphenols) on pasting properties of fresh and aged rice were investigated using Rapid Visco Analyzer. Results showed that ascorbic acid did not only significantly increase peak viscosity (PV) and breakdown of aged rice in a concentration dependent manner (p<0.05), but also decreased its setback significantly (p<0.05). Dithiothreitol increased the PV, breakdown and setback of the aged rice. Importantly, the extent of ascorbic acid enhancing PV of the aged rice was higher than that of dithiothreitol, and showed positive dose-effect relationship. Compared with ascorbic acid and dithiothreitol, tea polyphenols only significantly decreased setback of the aged rice (p<0.05). It was concluded that ascorbic acid was the most effective improver on pasting properties of aged rice as compared to dithiothreitol or tea polyphenols, especially in increasing PV and breakdown, and in decreasing setback. This showed rice ageing included, but was not limited, to the formation of disulfides, and more changes of ageing would involve hydrogen bonding and hydrophobic interactions. The different influences of SDS on fresh rice and aged rice also confirmed these findings to a certain extent. The improved role of ascorbic acid was ascribed to enhancing water absorption capacity, soluble solid content and granule swelling capacity of the aged rice.